Efficacy of Gegen Qinlian decoction plus metformin for type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials.

Gegen Qinlian Decoction (GQD) is frequently used as an adjunctive therapy to metformin for type 2 diabetes mellitus (T2DM), but the certainty and consistency of the supporting clinical evidence remain unclear. We searched CNKI, Wanfang Data, PubMed, EMBASE, Web of Science, and the Cochrane Central Register of Controlled Trials from database inception to January 31, 2026. Randomized controlled trials comparing GQD plus metformin with metformin alone in adults with T2DM were included. The primary outcome was glycated hemoglobin (HbA1c), and secondary outcomes were fasting plasma glucose (FPG) and 2-hour postprandial glucose (2hPG). Risk of bias was assessed using the Cochrane RoB 2 tool, and the certainty of evidence was evaluated using the GRADE framework. Random-effects meta-analyses were performed, with the primary analyses based on change-from-baseline values. Eight randomized controlled trials involving 725 participants were included. In the primary change-score analysis, GQD plus metformin did not show a statistically significant reduction in HbA1c compared with metformin alone (mean difference [MD] = -1.92, 95% confidence interval [CI]: -4.43 to 0.59, P = 0.13). Statistically significant reductions were observed for FPG (MD = -1.08, 95% CI: -1.71 to -0.44, P = 0.0009) and 2hPG (MD = -1.73, 95% CI: -3.05 to -0.42, P = 0.010). However, substantial heterogeneity was present across analyses (I² = 85%-100%), and the certainty of evidence was rated as very low because of risk of bias, inconsistency, and imprecision. Post-treatment sensitivity analyses using all eight trials showed statistically significant reductions in HbA1c, FPG, and 2hPG, but these analyses were also affected by substantial heterogeneity and high risk of bias across the included trials. Current evidence is insufficient to confirm a reliable clinical benefit of GQD as an adjunct to metformin for T2DM. Although reductions in FPG and 2hPG were observed, these findings should be interpreted as exploratory because of substantial heterogeneity, methodological limitations, and very low certainty of evidence. Larger, prospectively registered, well-designed, and adequately blinded randomized trials are needed.